Cozzolino, LorenzoNicastro, KatySeuront, LaurentMcQuaid, Christopher D.Zardi, Gerardo I.2023-03-012023-03-0120220048-9697http://hdl.handle.net/10400.1/19172Our understanding of how anthropogenic stressors such as climate change and plastic pollution interact with biodiver-sity is being widened to include diversity below the species level, i.e., intraspecific variation. The emerging apprecia-tion of the key ecological importance of intraspecific diversity and its potential loss in the Anthropocene, further highlights the need to assess the relative importance of intraspecific versus interspecific diversity. One such issue is whether a species responds as a homogenous whole to plastic pollution. Using manipulative field transplant experi-ments and laboratory-controlled hydrodynamic simulations, we assessed the relative effects of intraspecific and inter -specific diversity on microplastic trapping in coastal biogenic habitats dominated by two key bioengineers, the brown intertidal macroalgae Fucus vesiculosus and F. guiryi. At the individual level, northern morphotypes of F. guiryi trapped more microplastics than southern individuals, and F. vesiculosus trapped more microplastics than F. guiryi. Canopy den-sity varied among species, however, leading to reversed patterns of microplastic accumulation, with F. guiryi canopies accumulating more microplastics than those of F. vesiculosus, while no differences were observed between the canopies of F. guiryi morphotypes. We emphasize the importance of assessing the effects of intraspecific variation which, along with other crucial factors such as canopy density, flow velocity and polymer composition, modulates the extent of microplastic accumulation in coastal biogenic habitats. Our findings indicate that a realistic estimation of plastic accu-mulation in biogenic habitats requires an understanding of within-and between-species traits at both the individual and population levels.engMacroalgaeFucusPhenotypicGenotypicVariationFlumejournal article10.1016/j.scitotenv.2022.157771